to protect guam and likely within range of that north korean missile. the thad system using truck interceptors. >> i don't want to be the secretary of defense who was wrong once. and warplanes including fighter jets, u2 spy plane and attack jets in the skies as part of a massive military exercise. this morning, including practice in case of a chemical weapons attack. north korea has one of the largest chemical weapons stockpiles in the world. of course, the biggest threat is a nuclear weapon or a missile. we asked the head of u.s. forces here in south korea whether the north koreans had a nuclear weapon they could put on a missile. he said, we are not certain, but we have to take the threat seriously. of course, if they did launch some sort of nuclear weapon, it would be suicide for the north korean leader. george and robin? >> it sure would. okay, martha, thanks. more from our chief white house correspondent jonathan karl. jon, a delicate balancing act. they want to deter north korea, defend against the possible attack but have to be careful about prov